If for somereason all the humans in NY city were to just up and leave there would be a huge biological impact. rats, cats, dogs, birds, trees, and butterflies would be disrupted by lack of food, changes in water, reduction of the temperature island, heated underground spaces, lack of trash. Predators formerly finding the human habitation uninviting would swarm into the area.

Likewise formerly unfit mutants on some species, such as cockroaches in bright colors that were out in the daytime might appear

I'm somewhat skeptical that every observed change in Fukashima is casued by radition, even the new appearance of mutations. the departure of the human population might well be a catalyst as well.

I can guarantee that if they studied the impact of various chemical spills and other impacts left behind by the tsunami, they would find orders of magnitude more 'genetic impacts' than anything they'll find due to radiation. Problem is, nobody cares to do that study because there is no agenda driving it, and no funding, and no press would care.